We Keep Coding

How to include a third-party jar-file in compilation and runtime using command prompt in Windows 10?

I'm trying to understand the inclusion of third party jar files in a java project using only the command line in Windows 10.
Specifically, I try to include the file json-20200518.jar in my "project" so that I can use the java object JSONObject in the project.
My java file:
package com.mypackage.example;
import org.json.JSONObject;
class Example {
public static void main(String[] args) {
// ... program logic
}
}
location of my java file (Examp.java):
./com/mypackage/example
location of jar file:
./jars
using cmd win10 I compile:
javac -cp "C:\Users\pfort\Desktop\java\jars\json-20200518.jar" "C:\Users\pfort\Desktop\java\com\mypackage\example\Examp.java"
compilation is successful.
Run:
java -cp "C:\Users\pfort\Desktop\java\jars\json-20200518.jar" com.mypackage.example.Examp
I get a report:
Error: Could not find or load main class com.mypackage.example.Pokus
Caused by: java.lang.ClassNotFoundException: com.mypackage.example.Pokus
Second attempt:
java -cp "C:\Users\pfort\Desktop\java\jars\json-20200518.jar" "C:\Users\pfort\Desktop\java\com\mypackage\example\Pokus"
But the same error message comes back to me.
Where am I going wrong? Is it the wrong structure? I don't get it, the compilation is successful but the run does not work.

The compiled Examp.class file isn't part of json-20200518.jar, so you'll need to add the directory containing it to the command line. Assuming it's the current directory (.):
java -cp "C:\Users\pfort\Desktop\java\jars\json-20200518.jar;." com.mypackage.example.Examp

Jar Class not found upon execution

I am trying to use the javax.jms library: https://docs.oracle.com/javaee/7/api/javax/jms/package-summary.html, for which I have downloaded the jar: http://www.java2s.com/Code/Jar/j/Downloadjavaxjms111sourcesjar.htm
Specifically, I am trying to use the MessageListener and Message classes, which I know to be in there based on the Jar decompilation. I put this jar file next to my java file, so that the file structure looks like this:
myDir
-|jms.jar
-|Main.java
Main.java:
import javax.jms.MessageListener;
import javax.jms.Message;
public class Main {
public static void main(String[] args) {
MessageListener listener = new MessageListener() {
#Override
public void onMessage(Message msg) {
}
};
System.out.println("Hello World");
}
}
I can compile this using javac -cp jms.jar Main.java from inside myDir. This creates Main.class. However, when I run java Main, I get:
Exception in thread "main" java.lang.NoClassDefFoundError: javax/jms/MessageListener
This would lead me to believe that MessageListener is not included in the jar, but it is and the file structure is javax/jms/MessageListener checks out. What dumb mistake am I making?
When I compile without -cp js, it fails, saying:
error: package javax.jms does not exist
thus, at least the compiler is looking in the jar.

I made 2 Mistakes
1: Credit to #NormR, .:jms.jar (or .; for Windows I surmise)
2: Link jar while executing. Therefore, the commands should've been:
javac -cp .:jms.jar Main.java
java -cp .:jms.jar Main

How do I pass an additional jar do my java command when running application?

I have a java gradle projectA that references another java gradle projectB, that builds as a lib.
My gradle build configuration seems to be fine, since I can import and use classes from the other project, and it compiles. But when I try to run the application from the command line I get an error...
Exception in thread "main" java.lang.NoClassDefFoundError:
dawcore/SamplerInstrument at DawCLI.main(DawCLI.java:17) Caused by:
java.lang.ClassNotFoundException: dawcore.SamplerInstrument at
java.net.URLClassLoader.findClass(URLClassLoader.java:382) at
java.lang.ClassLoader.loadClass(ClassLoader.java:424) at
sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) at
java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 1 more
It seems to be complaining that it can't load the classes in the jar at runtime....which makes sense. But I don't know how to have it successfully load those classes.
my current run command that does not reference the jar, is as follows....
/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/bin/java -ea -cp "build/classes/main/" DawCLI
Running this gives the initially mentioned error.
I then read the docs on java -cp argument. It says to provide additional classpath directories, to separate them by semicolon.
I susequently updated my run command to be as follows....
/usr/lib/jvm/java-1.8.0-openjdk-amd64/jre/bin/java -ea -cp "build/classes/main/;../DawCore/build/libs/DawCore.jar" DawCLI
This gives me the following error....
Error: Could not find or load main class DawCLI
My main function is as follows..
import dawcore.*;
public class DawCLI {
public static void main (String [] args) throws IOException {
SamplerInstrument samplerkick = new SamplerInstrument();
}
}
According to the docs I seem to be doing this correctly, but am still getting errors. Any insight on this would be greatly appreciated!
Thanks

The solution was to replace the delimiting semi-colon with a colon instead. Even though the first line of the javadocs on -cp command indicate that you should use a semi-colon.
This could be because I am running on linux and those docs indicate Windows.
https://docs.oracle.com/javase/7/docs/technotes/tools/windows/java.html

Understanding JARs and Packages in Java

I'm trying to understand how jars and packages work in Java. So to do this, I created a simple test JAR and am trying to use a class contained in that jar. Simple enough, but it is giving me errors like "class not found". Here's the setup:
1) I have a file called MyHelloWorld.java, which will be packaged in a JAR:
package com.mytest;
public class MyHelloWorld {
public String getHello() {
return "Hello";
}
public static void main(String[] args) {
System.out.println("Hello world!");
}
}
2) I have another file called 'HelloHello.java' which uses the function getHello() in com.mytest.MyHelloWorld
import com.mytest.*;
public class HelloHello {
public static void main (String[] args) {
MyHelloWorld hello = new MyHelloWorld();
System.out.println(hello.getHello());
}
}
3) To package the MyHelloWorld class inside a JAR, I created the folders com/mytest in the current directory, and moved MyHelloWorld.java to that folder
4) I compiled MyHelloWorld.java in that folder using javac MyHelloWorld.java
5) I ran jar -cf myhello.jar ./com/mytest/*.class from the root folder to create the JAR file (as described in http://www.javacoffeebreak.com/faq/faq0028.html)
6) I copied HelloHello.java and myhello.jar to a new folder with nothing else in it, to test this setup
7) javac -cp ./*.jar HelloHello.java [succeeds]
8) java -cp ./*.jar HelloHello [FAILS] (I also tried just `java HelloWorld', which failed too, with a different error message)
This last statement fails with the message:
$java -cp ./*.jar HelloHello
Exception in thread "main" java.lang.NoClassDefFoundError: HelloHello
Caused by: java.lang.ClassNotFoundException: HelloHello
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:315)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:330)
at java.lang.ClassLoader.loadClass(ClassLoader.java:250)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:398)
Any idea why it's failing? Any insights you can provide on why it works this way, and how package names are defined inside a JAR etc. would also be appreciated!

I believe it is looking in the jar for your HelloHello class. You probably need the current folder on the classpath too.
java -cp .:myhello.jar HelloHello

You should use:
java -cp .:./* HelloHello
java and javac treat -cp argument a bit differently. With java the * in cp will automatically load all the jars it finds in the given location.
Also, the colon : is the separator between different classpath elements.

Make sure if HelloHello.class is in appropriate directories structure (com/mytest) than change your 8th step:
8) java com.mytest.HelloHello //or java -cp .;*.jar com.mytest.HelloHello

well, java HelloHello works too

Using a jar in a Java project?

I'm trying to use the public methods/classed from a project provided as a jar file (called Hello.jar for instance) wrapped in a package called hello.
package hello;
public class Hello
{
public static void main(String[] args)
{
coucou();
}
public static void coucou()
{
System.out.println("Hello there");
}
}
In a separate project called Tool, I want to be able to call the method Hello.coucou() so I wrote something like this:
import hello.*;
public class Tool
{
public static void main(String[] args)
{
System.out.println("main program running");
Hello.coucou();
}
}
and I compiled Tool.java with the following command (under linux):
$ javac Tool.java -classpath .:./extern/:
where Hello.jar is located in the folder ./extern
This seems to compile fine but when I launch it (i.e. java Tool), I get this:
main program running
Exception in thread "main" java.lang.NoClassDefFoundError: hello/Hello
at Tool.main(Tool.java:9)
Caused by: java.lang.ClassNotFoundException: hello.Hello
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:336)
... 1 more
I am new to Java (C/C++ background) and I don't understand what I'm doing wrong.
Any ideas?
Cheers
David
Edit: I tried adding Hello.jar to the classpath on the command line, but I still get the same error:
$ javac Tool.java -classpath .:./extern/Hello.jar:
$ java Tool -classpath .:./extern/Hello.jar:
main program running
Exception in thread "main" java.lang.NoClassDefFoundError: hello/Hello
at Tool.main(Tool.java:9)
Caused by: java.lang.ClassNotFoundException: hello.Hello
at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:336)
... 1 more

You need the Hello.jar on the classpath when you run as well as when you compile.

Actually the trick was in the order of the arguments in the command line:
Is the -cp (or -classpath) is set last, then it doesn't work
java Tool -cp .:extern/Hello.jar
It has to be first like:
java -cp .:extern/Hello.jar Tool
!!!

Java uses dynamic late binding, so putting the JAR in the classpath during compilation is only necessary to ensure that your code is using the classes from it correctly, but it does not actually embed them into your code as the linker would in C/C++. Thus, you need to set the classpath also when executing the code.
However, this:
$ javac Tool.java -classpath .:./extern/:
should not work either, since JARs need to be put into the classpath directly, not just the directory they live in:
$ javac Tool.java -classpath .:./extern/Hello.jar
Finally, you are placing your code in the default nameless package. This is OK for fooling around, but will cause problems in the long run (for one thing, you cannot import classes FROM the default package anywhere else).

When you run Java you must add the jar file too (adding the directory path only does not work).
See classpath information.
It should be something like this:
java -classpath /java/MyClasses/myclasses.jar utility.myapp.Cool

You need to include the Hello.jar file in the classpath when you launch it too.

java -cp xxx.jar hello where xxx is the jar you want to have in your classpath, if you want multiple jars then separate them using ;
karl